Color stable red-emitting phosphors

ABSTRACT

includes gradually adding a first solution comprising a source of M and HF and a second solution comprising a source of Mn to a reactor, in the presence of a source of A and an anion selected from phosphate, sulfate, acetate, and combinations thereof, to form a product liquor comprising the Mn+4 doped phosphor. The process also includes gradually discharging the product liquor from the reactor while volume of the product liquor in the reactor remains constant. A is Li, Na, K, Rb, Cs, or a combination thereof; M is Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Y, La, Nb, Ta, Bi, Gd, or a combination thereof; x is the absolute value of the charge of the [MFy] ion; and y is 5, 6 or 7.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to prior-filed, commonly owned,copending U.S. Provisional Application 62/472,135, filed 16 Mar. 2017,which is herein incorporated by reference.

BACKGROUND

Red-emitting phosphors based on complex fluoride materials activated byMn⁴⁺, such as those described in U.S. Pat. No. 7,358,542, U.S. Pat. No.7,497,973, and U.S. Pat. No. 7,648,649, can be utilized in combinationwith yellow/green emitting phosphors such as YAG:Ce to achieve warmwhite light (CCT<5000 K on the blackbody locus, color rendering index(CRI)>80) from a blue LED, equivalent to that produced by currentfluorescent, incandescent and halogen lamps. These materials absorb bluelight strongly and efficiently emit in a range between about 610 nm and658 nm with little deep red/NIR emission. Therefore, luminous efficacyis maximized compared to red phosphors that have significant emission inthe deeper red where eye sensitivity is poor. Quantum efficiency (QE)can exceed 85% under blue (440-460 nm) excitation. In addition, use ofthe red phosphors for displays can yield high gamut and efficiency.

Processes for preparing the materials described in the patent andscientific literature typically involve mixing the raw materials andprecipitating the product. Some examples of such batch processes aredescribed in Paulusz, A. G., J. Electrochem. Soc., 942-947 (1973), U.S.Pat. No. 7,497,973, and U.S. Pat. No. 8,491,816. However, scale-upissues and batch to batch variation of properties of the product can bea problem. Moreover, batch processes can produce materials having abroad range of particles sizes including relatively large particles.Large particles may clog dispensing equipment, causing problems inmanufacturing LED packages, and also tend to settle unevenly, resultingin a non-homogeneous distribution. Therefore, processes for preparingthe red phosphor that can allow better control over the final propertiesof the product while maintaining performance in lighting and displayapplications, are desirable.

BRIEF DESCRIPTION

In one example, the inventive subject matter disclosed herein provides aprocess for preparing a Mn⁺⁴ doped phosphor of formula I

where the process includes gradually adding a first solution comprisinga source of M and HF and a second solution comprising a source of Mn toa reactor, in the presence of a source of A and an anion selected fromphosphate, sulfate, acetate, and combinations thereof, to form a productliquor comprising the Mn⁺⁴ doped phosphor. The process also includesgradually discharging the product liquor from the reactor while volumeof the product liquor in the reactor remains constant. A is Li, Na, K,Rb, Cs, or a combination thereof; M is Si, Ge, Sn, Ti, Zr, Al, Ga, In,Sc, Y, La, Nb, Ta, Bi, Gd, or a combination thereof; x is the absolutevalue of the charge of the [MF_(y)] ion; and y is 5, 6 or 7.

The inventive subject matter described herein also provides a Mn⁺⁴ dopedphosphor of formula I prepared by this process, as well as a lightingapparatus and a backlight device that includes this Mn⁺⁴ doped phosphor.

In another example, the inventive subject matter described hereinprovides a process for preparing a Mn+⁴ doped phosphor of formula I,where the process includes gradually adding a first solution comprisinga source of M and HF and a second solution comprising a source of Mn toa reactor, in the presence of a source of A and a source of an anionselected from phosphate, sulfate, acetate, and combinations thereof, toform a product liquor comprising the Mn⁺⁴ doped phosphor, wherein thesource of the anion is an acid, a salt, or a combination thereof. Theprocess also includes gradually discharging the product liquor from thereactor while volume of the product liquor in the reactor remainsconstant. A is Li, Na, K, Rb, Cs, or a combination thereof; M is Si, Ge,Sn, Ti, Zr, Al, Ga, In, Sc, Y, La, Nb, Ta, Bi, Gd, or a combinationthereof x is the absolute value of the charge of the [MF_(y)] ion; and yis 5, 6 or 7.

A Mn⁺⁴ doped phosphor of formula I prepared by this process, as well asa lighting apparatus and a backlight device that includes the Mn′ dopedphosphor also are described herein.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a schematic cross-sectional view of a lighting apparatus inaccordance with one embodiment of the invention;

FIG. 2 is a schematic cross-sectional view of a lighting apparatus inaccordance with another embodiment of the invention;

FIG. 3 is a schematic cross-sectional view of a lighting apparatus inaccordance with yet another embodiment of the invention;

FIG. 4 is a cutaway side perspective view of a lighting apparatus inaccordance with one embodiment of the invention;

FIG. 5 is a schematic perspective view of a surface-mounted device (SMD)backlight LED.

DETAILED DESCRIPTION

The Mn⁴⁺ doped phosphors described herein are complex fluoridematerials, or coordination compounds, containing at least onecoordination center, surrounded by fluoride ions acting as ligands, andcharge-compensated by counter ions as necessary. For example,K₂SiF₆:Mn⁴⁺, the coordination center is Si and the counterion is K.Complex fluorides are occasionally written as a combination of simple,binary fluorides but such a representation does not indicate thecoordination number for the ligands around the coordination center. Thesquare brackets (occasionally omitted for simplicity) indicate that thecomplex ion they encompass is a new chemical species, different from thesimple fluoride ion. The activator ion (Mn⁴⁺) also acts as acoordination center, substituting for part of the centers of the hostlattice, for example, Si. The host lattice (including the counter ions)may further modify the excitation and emission properties of theactivator ion.

In particular embodiments, the coordination center of the phosphor, thatis, M in formula I, is Si, Ge, Sn, Ti, Zr, or a combination thereof.More particularly, the coordination center is Si, Ge, Ti, or acombination thereof, and the counterion, or A in formula I, is Na, K,Rb, Cs, or a combination thereof, and y is 6. Examples of phosphors offormula I include Examples of phosphors of formula I includeK₂[SiF₆]:Mn⁴⁺, K₂[TiF₆]:Mn⁴⁺, K₂[SnF₆]:Mn⁴⁺, Cs₂[TiF₆], Rb₂[TiF₆]:Mn⁴⁺,Cs₂[SiF₆]:Mn⁴⁺, Rb₂[SiF₆]:Mn⁴⁺, Na₂[TiF₆]:Mn⁴⁺, Na₂[ZrF₆]:Mn⁴⁺,K₃[ZrF₇]:Mn⁴⁺, K₃[BiF₆]:Mn⁴⁺, K₃[YF₆]:Mn⁴⁺, K₃[LaF₆]:Mn⁴⁺,K₃[GdF₆]:Mn⁴⁺, K₃[NbF₇]:Mn⁴⁺, K₃[TaF₇]:Mn⁴⁺. In particular embodiments,the phosphor of formula I is K₂SiF₆:Mn⁴⁺.

The amount of manganese in the Mn⁴⁺ doped phosphors of formula I mayrange from about 1.2 mol % (about 0.3 wt %) to about 16.5 mol % (about 4wt %). In particular embodiments, the amount of manganese may range fromabout 2 mol % (about 0.5 wt %) to 13.4 mol % (about 3.3 wt %), or fromabout 2 mol % to 12.2 mol % (about 3 wt %), or from about 2 mol % to11.2 mol % (about 2.76 wt %), or from about 2 mol % to about 10 mol %(about 2.5 wt %), or from about 2 mol % to 5.5 mol % (about 1.4 wt %),or from about 2 mol % to about 3.0 mol % (about 0.75 wt %).

A process according to the present invention includes gradually adding afirst solution that contains aqueous HF and a source of M and a secondsolution that contains a source of Mn to a reactor in the presence of asource of A to form a product liquor comprising the Mn⁴⁺ doped phosphorof formula I, and periodically discharging the product liquor from thereactor. Feed solutions include at least the first and second solutions,along with other solutions that may be added to the reactor before orduring the discharging. A process according to the present inventionincludes gradually adding a first solution that contains aqueous HF anda source of M and a second solution that contains a source of Mn to areactor in the presence of a source of A while gradually discharging theproduct liquor from the reactor. Discharging of at least a portion ofthe product liquor occurs contemporaneously with addition of the firstand second solution. Volume of the product liquor in the reactor ismaintained at an equilibrium level by discharging the product liquor atabout the same rate that feed solutions are added to the reactor. Feedsolutions include at least the first and second solutions, along withother solutions that may be added to the reactor before or during thedischarging.

Optionally, the process may include gradually adding a first solutionthat contains aqueous HF and a source of M and a second solution thatcontains a source of Mn to a reactor in the presence of a source of A.Volume of the product liquor in the reactor is maintained at anequilibrium level by discharging the product liquor at about the samerate that feed solutions are added to the reactor. Feed solutionsinclude at least the first and second solutions, along with othersolutions that may be added to the reactor before or during thedischarging. In some embodiments, the feed solutions may be added to thereactor during an initial period when the reactor is filled to anequilibrium volume without discharging the product liquor. Theequilibrium volume is the volume that remains substantially constantwhile the product liquor is discharged, and is approximately equal tothe amount of feed solutions that are added to the reactor in fiveminutes, particularly in three minutes, more particularly in twominutes, and even more particularly in one minute. The equilibriumvolume may be less than 35% of the total volume of all feed solutions,particularly less than 25% of the total volume of all feed solutions,and more particularly less than 15% of the total volume of all feedsolutions. In embodiments where the total amount of feed solution isabout 1000 mL, the equilibrium volume may range from about 70-200 mL,particularly from about 100-150 mL. Volume of the product liquor remainsconstant from the time that discharging of the product liquor beginsuntil the discharging is discontinued, or until addition of all feeds iscomplete or otherwise discontinued. After discharging has begun, therate of discharge is approximately the same as the total rate ofaddition of all feeds into the reactor so that the volume of the productliquor remains approximately constant during the discharge period. Inthe context of the present invention, ‘remains approximately constant’means that the volume of the product liquor varies less than about 50%over the time period when the product liquor is being discharged,particularly about 20%, and more particularly about 10%. The reactiontime, that is, the length of the addition and discharge periods, is notcritical. In some embodiments, it may range from about one hour to abouttwo hours. In some embodiments, the feed rates may be set to produceabout 10 g product per minute. The feed rate, discharge rate, andequilibrium volume may be chosen so that residence time of the productphosphor in the reactor ranges from about 5 seconds to about 10 minutes,particularly from about 30 seconds to about 5 minutes, more particularlyabout 30 seconds to about 2 minutes, even more particularly about oneminute.

In one or more embodiments, the process includes gradually adding thefirst solution that contains aqueous HF and the source of M and thesecond solution that contains the source of Mn to the reactor in thepresence of the source of A and an anion selected from phosphate,sulfate, acetate, and combinations thereof, to form a product liquorcomprising the Mil′ doped phosphor of formula I, and periodicallydischarging the product liquor from the reactor. The first solution andthe second solution can be added to the reactor in the presence of thesource of A and the anion and, optionally, a cation selected from H, Li,Na, K, Rb, Cs, or a combination thereof. The first and/or secondsolution can include the H⁺ and A⁺ cations. The anion and/or cation maybe obtained from an acid, such as sulfuric acid, phosphoric acid,hydrochloric acid, nitric acid, hydrobromic acid, hydriodic acid, orperchloric acid; or from potassium sulfate, a potassium acetate, oranother potassium source.

Gradually adding the first solution and the second solution to thereactor can include continually adding the first and second solutions(e.g., without interruption) to the reactor until the entire amounts ofthe first and second solutions to be used are in the reactor.Optionally, the first and/or second solutions may be gradually added tothe reactor in a non-continual or semi-continuous manner, such as byperiodically or irregularly adding the first and/or second solutions tothe reactor. For example, a first portion of the first and/or secondsolutions may be added to the reactor, followed by stopping the additionof the first and/or second solutions to the reactor, followed by addinga different, second portion of the first and/or second solution to thereactor, followed by stopping the addition of the first and/or secondsolutions to the reactor, and so on, until the entire amounts of thefirst and second solutions to be used are in the reactor.

In some embodiments, the feed solutions may be added to the reactorduring an initial period without discharging the product liquor. In someembodiments, the reactor may be precharged with a material selected fromHF, a source of A, preformed particles of the Mn⁺⁴ doped phosphor or theundoped host, or a combination thereof. A non-solvent or antisolvent forthe phosphor product may also be included in the precharge. Suitablematerials for the antisolvent include acetone, acetic acid, isopropanol,ethanol, methanol, acetonitrile, dimethyl formamide, or a combinationthereof. Alternatively, the antisolvent may be included in any of thefeed solutions, or in a separate feed solution without a source of M orMn, particularly in a feed solution that includes a source of A withouta source of M or Mn.

In one embodiment, a process according to the present invention mayminimize (or reduce relative to another process, such as a batchprocess) the amount of raw materials used to prepare the phosphors offormula I. In particular, the amount of toxic materials such as HF usedmay be significantly reduced in comparison with a batch process. Wherethe amount of HF is reduced, the product liquor may contain a higherlevel of raw materials compared to a batch process. In many embodiments,the product liquor contains at least 10% dissolved solids, particularlyat least 19% dissolved solids, after the start of the discharge.Additionally, product yields may be higher compared batch processes. Forexample, product yield from processes according to the present inventionmay be as high as 85-95%, whereas yields from batch processes aretypically in the range of 60%-75%.

After the initial period, at least a portion of the product liquor maybe discharged. Addition of the feed solutions may be continued while theproduct liquor is discharged, although, in some embodiments, it may bedesirable to suspend the addition during the discharge period. Thelength of each addition period before or between discharge eventstypically ranges between 2 and 30 minutes, particularly between 5-15minutes, more particularly 8-12 minutes. Longer addition periods mayresult in larger particles, and/or degradation of the product, resultingin loss of desirable properties such as brightness. The total reactiontime, that is, the total length of tall addition periods, is notcritical. In some embodiments, it may be about one hour.

The first solution includes aqueous HF and a source of M. The source ofM may be a compound containing Si, having good in solubility in thesolution, for example, H₂SiF₆, Na₂SiF₆, (NH₄)₂SiF₆, Rb₂SiF₆, Cs₂SiF₆,SiO₂ or a combination thereof, particularly H₂SiF₆. Use of H₂SiF₆ isadvantageous because it has very high solubility in water, and itcontains no alkali metal element as an impurity. The source of M may bea single compound or a combination of two or more compounds. The HFconcentration in the first solution may be at least 25 wt %,particularly at least 30 wt %, more particularly at least 35 wt %. Watermay be added to the first solution, reducing the concentration of HF, todecrease particle size and improve product yield. Concentration of thematerial used as the source of M may be ≤25 wt %, particularly ≤15 wt %.

The second solution includes a source of Mn, and may also includeaqueous HF as a solvent. Suitable materials for use as the source of Mninclude for example, K₂MnF₆, KMnO₄. K₂MnCl₆, MnF₄, MnF₃, MnF₂, MnO₂, andcombinations thereof, and, in particular, K₂MnF₆. Concentration of thecompound or compounds used as the source of Mn is not critical; and istypically limited by its solubility in the solution. The HFconcentration in the second solution may be at least 20 wt %,particularly at least 40 wt %.

The first and second solutions are added to the reactor in the presenceof a source of A while stirring the product liquor. Amounts of the rawmaterials used generally correspond to the desired composition, exceptthat an excess of the source of A may be present. Flow rates may beadjusted so that the sources of M and Mn are added in a roughlystoichiometric ratio while the source of A is in excess of thestoichiometric amount. In many embodiments, the source of A is added inan amount ranging from about 150% to 300% molar excess, particularlyfrom about 175% to 300% molar excess. For example, in Mn-doped K₂SiF₆,the stoichiometric amount of K required is 2 moles per mole of Mn-dopedK₂SiF₆, and the amount of KF or KHF₂ used ranges from about 3.5 moles toabout 6 moles of the product phosphor.

The source of A may be a single compound or a mixture of two or morecompounds. Suitable materials include KF, KHF₂, KOH, KCl, KBr, Kl, KOCH₃or K₂CO₃, particularly KF and KHF₂ more particularly KHF₂. A source ofMn that contains K, such as K₂MnF₆, may be a K source, particularly incombination with KF or KHF₂. The source of A may be present in either orboth of the first and second solutions, in a third solution addedseparately, in the reactor pot, or in a combination of one or more ofthese.

After the product liquor is discharged from the reactor, the Mn⁺⁴ dopedphosphor may be isolated from the product liquor by simply decanting thesolvent or by filtration, and treated as described in U.S. Pat. No.8,252,613 or US 2015/0054400, with a concentrated solution of a compoundof formula II in aqueous hydrofluoric acid;

A¹ _(x)[MF_(y)]  (II)

wherein

A¹ is H, Li, Na, K, Rb, Cs, or a combination thereof;

M is Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Y, La, Nb, Ta, Bi, Gd, or acombination thereof;

x is the absolute value of the charge of the [MF_(y)] ion; and

y is 5, 6 or 7.

The compound of formula II includes at least the MF_(y) anion of thehost compound for the product phosphor, and may also include the A⁺cation of the compound of formula I. For a product phosphor of formulaMn-doped K₂SiF₆, suitable materials for the compound of formula IIinclude H₂SiF₆, Na₂SiF₆, (NH₄)₂SiF₆, Rb₂SiF₆, Cs₂SiF₆, or a combinationthereof, particularly H₂SiF₆, K₂SiF₆ and combinations thereof, moreparticularly K₂SiF₆. The treatment solution is a saturated or nearlysaturated of the compound of formula II in hydrofluoric acid. A nearlysaturated solution contains about 1-10% excess aqueous HF added to asaturated solution. Concentration of HF in the solution ranges fromabout 25% (wt/vol) to about 70% (wt/vol), in particular from about 40%(wt/vol) to about 50% (wt/vol). Less concentrated solutions may resultin reduced performance of the phosphor. The amount of treatment solutionused ranges from about 2-30 ml/g product, particularly about 5-20 ml/gproduct, more particularly about 5-15 ml/g product.

The treated phosphor may be vacuum filtered, and washed with one or moresolvents to remove HF and unreacted raw materials. Suitable materialsfor the wash solvent include acetic acid and acetone, and combinationsthereof.

Span is a measure of the width of the particle size distribution curvefor a particulate material or powder, and is defined according toequation (1):

$\begin{matrix}{{Span} = \frac{\left( {D_{90} - D_{10}} \right)}{D_{50}}} & (1)\end{matrix}$

wherein

-   -   D₅₀ is the median particle size for a volume distribution;    -   D₉₀ is the particle size for a volume distribution that is        greater than the particle size of 90% of the particles of the        distribution; and    -   D₁₀ is the particle size for a volume distribution that is        greater than the particle size of 10% of the particles of the        distribution.        Particle size of the phosphor powder may be conveniently        measured by laser diffraction methods, and software provided        with commercial instruments can generate D₉₀, D₁₀, and D₅₀        particle size values and span of the distribution. For phosphor        particles of the present invention, D₅₀ particle size ranges        from about 10 μm to about 40 particularly from about 15 μm to        about 35 more particularly from about 20 μm to about 30 Span of        the particle size distribution may be ≤1.0, particularly ≤0.9,        more particularly ≤0.8, and even more particularly ≤0.7.        Particle size may be controlled by adjusting flow rates,        reactant concentrations, and equilibrium volume of the product        liquor.

After the product phosphor is isolated from the product liquor, treatedand dried, it may be annealed to improve stability as described in U.S.Pat. No. 8,906,724. In such embodiments, the product phosphor is held atan elevated temperature, while in contact with an atmosphere containinga fluorine-containing oxidizing agent. The fluorine-containing oxidizingagent may be F₂, HF, SF₆, BrF₅, NH₄HF₂, NH₄F, KF, AlF₃, SbF₅, ClF₃,BrF₃, KrF₂, XeF₂, XeF₄, NF₃, SiF₄, PbF₂, ZnF₂, SnF₂, CdF₂ or acombination thereof. In particular embodiments, the fluorine-containingoxidizing agent is F₂. The amount of oxidizing agent in the atmospheremay be varied to obtain the color stable phosphor, particularly inconjunction with variation of time and temperature. Where thefluorine-containing oxidizing agent is F₂, the atmosphere may include atleast 0.5% F₂, although a lower concentration may be effective in someembodiments. In particular, the atmosphere may include at least 5% F₂and more particularly at least 20% F₂. The atmosphere may additionallyinclude nitrogen, helium, neon, argon, krypton, xenon, in anycombination with the fluorine-containing oxidizing agent. In particularembodiments, the atmosphere is composed of about 20% F₂ and about 80%nitrogen.

The temperature at which the phosphor is contacted with thefluorine-containing oxidizing agent is any temperature in the range fromabout 200° C. to about 700° C., particularly from about 350° C. to about600° C. during contact, and in some embodiments from about 500° C. toabout 600° C. The phosphor is contacted with the oxidizing agent for aperiod of time sufficient to convert it to a color stable phosphor. Timeand temperature are interrelated, and may be adjusted together, forexample, increasing time while reducing temperature, or increasingtemperature while reducing time. In particular embodiments, the time isat least one hour, particularly for at least four hours, moreparticularly at least six hours, and most particularly at least eighthours.

After holding at the elevated temperature for the desired period oftime, the temperature in the furnace may be reduced at a controlled ratewhile maintaining the oxidizing atmosphere for an initial coolingperiod. After the initial cooling period, the cooling rate may becontrolled at the same rate or a different rate, or may be uncontrolled.In some embodiments, the cooling rate is controlled at least until atemperature of 200° C. is reached. In other embodiments, the coolingrate is controlled at least until a temperature at which it is safe topurge the atmosphere is reached. For example, the temperature may bereduced to about 50° C. before a purge of the fluorine atmospherebegins. Reducing the temperature at a controlled rate of ≤5° C. perminute may yield a phosphor product having superior properties comparedto reducing the temperature at a rate of 10° C./minute. In variousembodiments, the rate may be controlled at ≤5° C. per minute,particularly at ≤3° C. per minute, more particularly at a rate of ≤1° C.per minute.

The period of time over which the temperature is reduced at thecontrolled rate is related to the contact temperature and cooling rate.For example, when the contact temperature is 540° C. and the coolingrate is 10° C./minute, the time period for controlling the cooling ratemay be less than one hour, after which the temperature may be allowed tofall to the purge or ambient temperature without external control. Whenthe contact temperature is 540° C. and the cooling rate is ≤5° C. perminute, then the cooling time may be less than two hours. When thecontact temperature is 540° C. and the cooling rate is ≤3° C. perminute, then the cooling time may be less than three hours. When thecontact temperature is 540° C. and the cooling rate is ≤1° C. perminute, then the cooling time is may be less than four hours. Forexample, the temperature may be reduced to about 200° C. with controlledcooling, then control may be discontinued. After the controlled coolingperiod, the temperature may fall at a higher or lower rate than theinitial controlled rate.

The manner of contacting the phosphor with the fluorine-containingoxidizing agent is not critical and may be accomplished in any waysufficient to convert the phosphor to a color stable phosphor having thedesired properties. In some embodiments, the chamber containing thephosphor may be dosed and then sealed such that an overpressure developsas the chamber is heated, and in others, the fluorine and nitrogenmixture is flowed throughout the anneal process ensuring a more uniformpressure. In some embodiments, an additional dose of thefluorine-containing oxidizing agent may be introduced after a period oftime.

The annealed phosphor may be treated with a saturated or nearlysaturated solution of a composition of formula II in aqueoushydrofluoric acid, as described in U.S. Pat. No. 8,252,613. The amountof treatment solution used ranges from about 10 ml/g product to 20 ml/gproduct, particularly about 10 ml/g product. The treated annealedphosphor may be isolated by filtration, washed with solvents such asacetic acid and acetone to remove contaminates and traces of water, andstored under nitrogen.

Any numerical values recited herein include all values from the lowervalue to the upper value in increments of one unit provided that thereis a separation of at least 2 units between any lower value and anyhigher value. As an example, if it is stated that the amount of acomponent or a value of a process variable such as, for example,temperature, pressure, time and the like is, for example, from 1 to 90,preferably from 20 to 80, more preferably from 30 to 70, it is intendedthat values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32 etc. areexpressly enumerated in this specification. For values which are lessthan one, one unit is considered to be 0.0001, 0.001, 0.01 or 0.1 asappropriate. These are only examples of what is specifically intendedand all possible combinations of numerical values between the lowestvalue and the highest value enumerated are to be considered to beexpressly stated in this application in a similar manner.

A lighting apparatus or light emitting assembly or lamp 10 according toone embodiment of the present invention is shown in FIG. 1. Lightingapparatus 10 includes a semiconductor radiation source, shown as lightemitting diode (LED) chip 12, and leads 14 electrically attached to theLED chip. The leads 14 may be thin wires supported by a thicker leadframe(s) 16 or the leads may be self-supported electrodes and the leadframe may be omitted. The leads 14 provide current to LED chip 12 andthus cause it to emit radiation.

The lamp may include any semiconductor blue or UV light source that iscapable of producing white light when its emitted radiation is directedonto the phosphor. In one embodiment, the semiconductor light source isa blue emitting LED doped with various impurities. Thus, the LED maycomprise a semiconductor diode based on any suitable III-V, II-VI orIV-IV semiconductor layers and having an emission wavelength of about250 to 550 nm. In particular, the LED may contain at least onesemiconductor layer comprising GaN, ZnSe or SiC. For example, the LEDmay comprise a nitride compound semiconductor represented by the formulaIn_(i)Ga_(j)Al_(k)N (where 0≤i; 0≤j; 0≤k and I+j+k=1) having an emissionwavelength greater than about 250 nm and less than about 550 nm. Inparticular embodiments, the chip is a near-uv or blue emitting LEDhaving a peak emission wavelength from about 400 to about 500 nm. SuchLED semiconductors are known in the art. The radiation source isdescribed herein as an LED for convenience. However, as used herein, theterm is meant to encompass all semiconductor radiation sourcesincluding, e.g., semiconductor laser diodes. Further, although thegeneral discussion of the exemplary structures of the inventiondiscussed herein is directed toward inorganic LED based light sources,it should be understood that the LED chip may be replaced by anotherradiation source unless otherwise noted and that any reference tosemiconductor, semiconductor LED, or LED chip is merely representativeof any appropriate radiation source, including, but not limited to,organic light emitting diodes.

In lighting apparatus 10, phosphor composition 22 is radiationallycoupled to the LED chip 12. Radiationally coupled means that theelements are associated with each other so radiation from one istransmitted to the other. Phosphor composition 22 is deposited on theLED 12 by any appropriate method. For example, a water based suspensionof the phosphor(s) can be formed, and applied as a phosphor layer to theLED surface. In one such method, a silicone slurry in which the phosphorparticles are randomly suspended is placed around the LED. This methodis merely exemplary of possible positions of phosphor composition 22 andLED 12. Thus, phosphor composition 22 may be coated over or directly onthe light emitting surface of the LED chip 12 by coating and drying thephosphor suspension over the LED chip 12. In the case of asilicone-based suspension, the suspension is cured at an appropriatetemperature. Both the shell 18 and the encapsulant 20 should betransparent to allow white light 24 to be transmitted through thoseelements. Although not intended to be limiting, in some embodiments, themedian particle size of the phosphor composition ranges from about 1 toabout 50 microns, particularly from about 15 to about 35 microns.

In other embodiments, phosphor composition 22 is interspersed within theencapsulant material 20, instead of being formed directly on the LEDchip 12. The phosphor (in the form of a powder) may be interspersedwithin a single region of the encapsulant material 20 or throughout theentire volume of the encapsulant material. Blue light emitted by the LEDchip 12 mixes with the light emitted by phosphor composition 22, and themixed light appears as white light. If the phosphor is to beinterspersed within the material of encapsulant 20, then a phosphorpowder may be added to a polymer or silicone precursor, loaded aroundthe LED chip 12, and then the polymer precursor may be cured to solidifythe polymer or silicone material. Other known phosphor interspersionmethods may also be used, such as transfer loading.

In some embodiments, the encapsulant material 20 is a silicone matrixhaving an index of refraction R, and, in addition to phosphorcomposition 22, contains a diluent material having less than about 5%absorbance and index of refraction of R±0.1. The diluent material has anindex of refraction of ≤1.7, particularly ≤1.6, and more particularly≤1.5. In particular embodiments, the diluent material is of formula II,and has an index of refraction of about 1.4. Adding an opticallyinactive material to the phosphor/silicone mixture may produce a moregradual distribution of light flux through the phosphor/encapsulantmixture and can result in less damage to the phosphor. Suitablematerials for the diluent include fluoride compounds such as LiF, MgF₂,CaF₂, SrF₂, AlF₃, K₂NaAlF₆, KMgF₃, CaLiAlF₆, K₂LiAlF₆, and K₂SiF₆, whichhave index of refraction ranging from about 1.38 (AlF₃ and K₂NaAlF₆) toabout 1.43 (CaF₂), and polymers having index of refraction ranging fromabout 1.254 to about 1.7. Non-limiting examples of polymers suitable foruse as a diluent include polycarbonates, polyesters, nylons,polyetherimides, polyetherketones, and polymers derived from styrene,acrylate, methacrylate, vinyl, vinyl acetate, ethylene, propylene oxide,and ethylene oxide monomers, and copolymers thereof, includinghalogenated and unhalogenated derivatives. These polymer powders can bedirectly incorporated into silicone encapsulants before silicone curing.

In yet another embodiment, phosphor composition 22 is coated onto asurface of the shell 18, instead of being formed over the LED chip 12.The phosphor composition is preferably coated on the inside surface ofthe shell 18, although the phosphor may be coated on the outside surfaceof the shell, if desired. Phosphor composition 22 may be coated on theentire surface of the shell or only a top portion of the surface of theshell. The UV/blue light emitted by the LED chip 12 mixes with the lightemitted by phosphor composition 22, and the mixed light appears as whitelight. Of course, the phosphor may be located in any two or all threelocations or in any other suitable location, such as separately from theshell or integrated into the LED.

FIG. 2 illustrates a second structure of the system according to thepresent invention. Corresponding numbers from FIGS. 1-4 (e.g. 12 inFIGS. 1 and 112 in FIG. 2) relate to corresponding structures in each ofthe figures, unless otherwise stated. The structure of the embodiment ofFIG. 2 is similar to that of FIG. 1, except that the phosphorcomposition 122 is interspersed within the encapsulant material 120,instead of being formed directly on the LED chip 112. The phosphor (inthe form of a powder) may be interspersed within a single region of theencapsulant material or throughout the entire volume of the encapsulantmaterial. Radiation (indicated by arrow 126) emitted by the LED chip 112mixes with the light emitted by the phosphor 122, and the mixed lightappears as white light 124. If the phosphor is to be interspersed withinthe encapsulant material 120, then a phosphor powder may be added to apolymer precursor, and loaded around the LED chip 112. The polymer orsilicone precursor may then be cured to solidify the polymer orsilicone. Other known phosphor interspersion methods may also be used,such as transfer molding.

FIG. 3 illustrates a third possible structure of the system according tothe present invention. The structure of the embodiment shown in FIG. 3is similar to that of FIG. 1, except that the phosphor composition 222is coated onto a surface of the envelope 218, instead of being formedover the LED chip 212. The phosphor composition 222 is preferably coatedon the inside surface of the envelope 218, although the phosphor may becoated on the outside surface of the envelope, if desired. The phosphorcomposition 222 may be coated on the entire surface of the envelope, oronly a top portion of the surface of the envelope. The radiation 226emitted by the LED chip 212 mixes with the light emitted by the phosphorcomposition 222, and the mixed light appears as white light 224. Ofcourse, the structures of FIGS. 1-3 may be combined, and the phosphormay be located in any two or all three locations, or in any othersuitable location, such as separately from the envelope, or integratedinto the LED.

In any of the above structures, the lamp may also include a plurality ofscattering particles (not shown), which are embedded in the encapsulantmaterial. The scattering particles may comprise, for example, alumina ortitania. The scattering particles effectively scatter the directionallight emitted from the LED chip, preferably with a negligible amount ofabsorption.

As shown in a fourth structure in FIG. 4, the LED chip 412 may bemounted in a reflective cup 430. The cup 430 may be made from or coatedwith a dielectric material, such as alumina, titania, or otherdielectric powders known in the art, or be coated by a reflective metal,such as aluminum or silver. The remainder of the structure of theembodiment of FIG. 4 is the same as those of any of the previousfigures, and can include two leads 416, a conducting wire 432, and anencapsulant material 420. The reflective cup 430 is supported by thefirst lead 416 and the conducting wire 432 is used to electricallyconnect the LED chip 412 with the second lead 416.

Another structure (particularly for backlight applications) is a surfacemounted device (“SMD”) type light emitting diode 550, e.g. asillustrated in FIG. 5. This SMD is a “side-emitting type” and has alight-emitting window 552 on a protruding portion of a light guidingmember 554. An SMD package may comprise an LED chip as defined above,and a phosphor material that is excited by the light emitted from theLED chip. Other backlight devices include, but are not limited to, TVs,computers, smartphones, tablet computers and other handheld devices thathave a display including a semiconductor light source; and a colorstable Mn⁴⁺ doped phosphor according to the present invention.

When used with an LED emitting at from 350 to 550 nm and one or moreother appropriate phosphors, the resulting lighting system will producea light having a white color. Lamp 10 may also include scatteringparticles (not shown), which are embedded in the encapsulant material.The scattering particles may comprise, for example, alumina or titania.The scattering particles effectively scatter the directional lightemitted from the LED chip, preferably with a negligible amount ofabsorption.

In addition to the color stable Mn⁴⁺ doped phosphor, phosphorcomposition 22 may include one or more other phosphors. When used in alighting apparatus in combination with a blue or near UV LED emittingradiation in the range of about 250 to 550 nm, the resultant lightemitted by the assembly will be a white light. Other phosphors such asgreen, blue, yellow, red, orange, or other color phosphors may be usedin the blend to customize the white color of the resulting light andproduce specific spectral power distributions. Other materials suitablefor use in phosphor composition 22 include electroluminescent polymerssuch as polyfluorenes, preferably poly(9,9-dioctyl fluorene) andcopolymers thereof, such aspoly(9,9′-dioctylfluorene-co-bis-N,N′-(4-butylphenyl)diphenylamine)(F8-TFB); poly(vinylcarbazole) and polyphenylenevinylene and theirderivatives. In addition, the light emitting layer may include a blue,yellow, orange, green or red phosphorescent dye or metal complex, or acombination thereof. Materials suitable for use as the phosphorescentdye include, but are not limited to, tris(1-phenylisoquinoline) iridium(III) (red dye), tris(2-phenylpyridine) iridium (green dye) and Iridium(III) bis(2-(4,6-difluorephenyl)pyridinato-N,C2) (blue dye).Commercially available fluorescent and phosphorescent metal complexesfrom ADS (American Dyes Source, Inc.) may also be used. ADS green dyesinclude ADS060GE, ADS061GE, ADS063GE, and ADS066GE, ADS078GE, andADS090GE. ADS blue dyes include ADS064BE, ADS065BE, and ADS070BE. ADSred dyes include ADS067RE, ADS068RE, ADS069RE, ADS075RE, ADS076RE,ADS067RE, and ADS077RE.

Suitable phosphors for use in phosphor composition 22 in addition to theMn⁴⁺ doped phosphor include, but are not limited to:

((Sr_(1−z) (Ca, Ba, Mg, Zn)_(z))_(1−(x+w))(Li, Na, K,Rb)_(w)Ce_(x))₃(Al_(1−y)Si_(y))O_(4+y+3(x−w))F_(1−y−3 (x−w)), 0<x≤0.10,0≤y≤0.5, 0≤z≤0.5, 0≤w≤x;(Ca, Ce)₃Sc₂Si₃O₁₂ (CaSiG);(Sr,Ca,Ba)₃Al_(1−x)Si_(x)O_(4+x)F_(1−x):Ce³⁺ (SASOF));(Ba,Sr,Ca)₅(PO₄)₃(Cl,F,Br,OH):Eu²⁺,Mn²⁺; (Ba,Sr,Ca)BPO₅:Eu²⁺,Mn²⁺;(Sr,Ca)₁₀(PO₄)₆*νB₂O₃:Eu²⁺ (wherein 0<ν≤1); Sr₂Si₃O₈*2SrCl₂:Eu²⁺;(Ca,Sr,Ba)₃MgSi₂O₈:Eu²⁺,Mn²⁺; BaAl₈O₁₃:Eu²⁺;2SrO*0.84P₂O₅*0.16B₂O₃:Eu²⁺; (Ba,Sr,Ca)MgAl₁₀O₁₇:Eu²⁺,Mn²⁺;(Ba,Sr,Ca)Al₂O₄:Eu²⁺; (Y,Gd,Lu,Sc,La)BO₃:Ce³⁺,Tb³⁺; ZnS:Cu⁺,Cl⁻;ZnS:Cu⁺,Al³⁺; ZnS:Ag⁺,Cl⁻; ZnS:Ag⁺,Al³⁺;(Ba,Sr,Ca)₂Si_(1−ξ)O_(4−2ξ):Eu²⁺ (wherein 0≤ξ≤0.2);(Ba,Sr,Ca)₂(Mg,Zn)Si₂O₇:Eu²⁺; (Sr,Ca,Ba)(Al,Ga,In)₂S₄:Eu²⁺;(Y,Gd,Tb,La,Sm,Pr,Lu)₃(Al,Ga)_(5−α)O_(12-3/2α):Ce³⁺ (wherein 0≤α≤0.5);(Ca,Sr)₈(Mg,Zn)(SiO₄)₄Cl₂:Eu²⁺,Mn²⁺; Na₂Gd₂B₂O₇:Ce³⁺,Tb³⁺;(Sr,Ca,Ba,Mg,Zn)₂P₂O₇:Eu²⁺,Mn²⁺; (Gd,Y,Lu,La)₂O₃:Eu³⁺,Bi³⁺;(Gd,Y,Lu,La)₂O₂S:Eu³⁺,Bi³⁺; (Gd,Y,Lu,La)VO₄:Eu³⁺,Bi³⁺; (Ca,Sr)S:Eu²⁺,Ce³⁺; SrY₂S₄:Eu²⁺; CaLa₂S₄:Ce³⁺; (Ba,Sr,Ca)MgP₂O₇:Eu²⁺,Mn²⁺;(Y,Lu)₂WO₆:Eu³⁺,Mo⁶⁺; (Ba,Sr,Ca)_(β)Si_(γ)N_(μ):Eu²⁺ (wherein 2β+4γ=3μ;Ca₃(SiO₄)Cl₂:Eu²⁺;(Lu,Sc,Y,Tb)_(2-u-v)Ce_(v)Ca_(1+u)Li_(w)Mg_(2-w)P_(w)(Si,Ge)_(3-w)O_(12-u/2)(where −0.5≤u≤1, 0<v≤0.1, and 0≤w≤0.2);(Y,Lu,Gd)_(2−α)Ca_(φ)Si₄N_(6+φ)C_(1−φ):Ce³⁺, (wherein 0≤φ≤0.5); (Ca,Sr,Ba)SiO₂N₂:Eu²⁺,Ce³⁺;(Lu,Ca,Li,Mg,Y) α-SiAlON doped with Eu²⁺ and/or Ce³⁺; β-SiAlON:Eu²⁺,3.5MgO*0.5MgF₂*GeO₂:Mn⁴⁺; Ca_(1−c−f)Ce_(c)Eu_(f)Al_(1+c) Si_(1−c)N₃,(where 0≤c≤0.2, 0≤f≤0.2);Ca_(1−h−r)Ce_(h)Eu_(r)Al_(1−h)(Mg,Zn)_(h)SiN₃, (where 0≤h≤0.2, 0≤r≤0.2);Ca_(1−2s−t)Ce_(s)(Li,Na)_(s)Eu_(t)AlSiN₃, (where 0≤s≤0.2, 0≤f≤0.2,s+t>0); andCa_(1−σ−χ−ϕ)Ce_(σ)(Li,Na)_(χ)Eu_(ϕ)Al_(1+σ−χ)Si_(1−σ+χ)N₃, (where0≤σ≤0.2, 0≤χ≤0.4, 0≤ϕ≤0.2).

In particular, phosphor composition 22 may include one or more phosphorsthat result in a green spectral power distribution under ultraviolet,violet, or blue excitation. In the context of the present invention,this is referred to as a green phosphor or green phosphor material. Thegreen phosphor may be a single composition or a blend that emits lightin a green to yellow-green to yellow range, such as cerium-doped yttriumaluminum garnets, more particularly (Y,Gd,Lu,Tb)₃(Al,Ga)₅O₁₂:Ce³⁺. Thegreen phosphor may also be a blend of blue- and red-shifted garnetmaterials. For example, a Ce³⁺-doped garnet having blue shifted emissionmay be used in combination with a Ce³⁺-doped garnet that has red-shiftedemission, resulting in a blend having a green spectral powerdistribution. Blue- and red-shifted garnets are known in the art. Insome embodiments, versus a baseline Y₃Al₅O₁₂:Ce³⁺ phosphor, ablue-shifted garnet may have Lu³⁺ substitution for Y³⁺, Ga³⁺substitution for Al³⁺, or lower Ce³⁺ doping levels in a Y₃Al₅O₁₂:Ce³⁺phosphor composition. A red-shifted garnet may have Gd³⁺/Tb³⁺substitution for Y³⁺ or higher Ce³⁺ doping levels. An example of a greenphosphor that is particularly useful for display application isβ-SiAlON.

The ratio of each of the individual phosphors in the phosphor blend mayvary depending on the characteristics of the desired light output. Therelative proportions of the individual phosphors in the variousembodiment phosphor blends may be adjusted such that when theiremissions are blended and employed in an LED lighting device, there isproduced visible light of predetermined x and y values on the CIEchromaticity diagram. As stated, a white light is preferably produced.This white light may, for instance, may possess an x value in the rangeof about 0.20 to about 0.55, and a y value in the range of about 0.20 toabout 0.55. As stated, however, the exact identity and amounts of eachphosphor in the phosphor composition can be varied according to theneeds of the end user. For example, the material can be used for LEDsintended for liquid crystal display (LCD) backlighting. In thisapplication, the LED color point would be appropriately tuned based uponthe desired white, red, green, and blue colors after passing through anLCD/color filter combination. The list of potential phosphor forblending given here is not meant to be exhaustive and these Mn⁴⁺-dopedphosphors can be blended with various phosphors with different emissionto achieve desired spectral power distributions.

In some embodiments, lighting apparatus 10 has a color temperature lessthan or equal to 4200 K, and phosphor composition 22 includes a redphosphor consisting of a color stable Mn⁴⁺ doped phosphor of formula I.That is, the only red phosphor present in phosphor composition 22 is thecolor stable Mn⁴⁺ doped phosphor; in particular, the phosphor isK₂SiF₆:Mn⁴⁺. The composition may additionally include a green phosphor.The green phosphor may be a Ce³⁺-doped garnet or blend of garnets,particularly a Ce³⁺-doped yttrium aluminum garnet, and moreparticularly, YAG having the formula (Y,Gd,Lu,Tb)₃(Al,Ga)₅O₁₂:Ce³⁺. Whenthe red phosphor is K₂SiF₆:Mn⁴⁺, the mass ratio of the red phosphor tothe green phosphor material may be less than 3.3, which may besignificantly lower than for red phosphors of similar composition, buthaving lower levels of the Mn dopant.

The color stable Mn⁴⁺ doped phosphors of the present invention may beused in applications other than those described above. For example, thematerial may be used as a phosphor in a fluorescent lamp, in a cathoderay tube, in a plasma display device or in a liquid crystal display(LCD). The material may also be used as a scintillator in anelectromagnetic calorimeter, in a gamma ray camera, in a computedtomography scanner or in a laser. These uses are merely exemplary andnot limiting.

EXAMPLES Comparative Examples 1 and 2: Preparation of Mn⁴⁺ Doped K₂SiF₆by Batch Process

Amounts and distribution of starting materials among Beakers A-D areshown in Table 1. Beaker A was stirred aggressively, and the contents ofbeaker B were added thereto dropwise over the course of about tenminutes. Dropwise addition of the contents of beaker C and D to beaker Awas started about one minute after the contents of beaker B was startedand continued over the course of about nine minutes. The precipitate wasdigested for 10 minutes and the stirring was stopped. The supernatantwas decanted, and the precipitate was vacuum filtered, rinsed once withacetic acid and twice with acetone, and then dried under vacuum. Thedried powder was sifted through a 325 mesh screen, and annealed under a20% F₂/80% nitrogen atmosphere for 8 hour at 540° C. The annealedphosphor was washed with a solution of 49% HF saturated with K₂SiF₆,dried under vacuum and sifted through a 325 mesh screen.

TABLE 1 Batch Process Raw Materials Solution A Solution B Solution CSolution D Comp. HF H₂SiF₆ HF HF HF Ex. KF KH₂F K₂MnF₆ (49%) (35%) (49%)K₂MnF₆ (49%) KF (49%) no. (g) (g) (g) (mL) (mL) (mL) (g) (mL) (g) (mL) 16.6 0.44 120.0 35.0 122.5 1.00 35.0 22.5 42.5 2 6.6 0.75 120.0 35.0 70.01.61 40.0 22.5 42.5

Example 1: Preparation of Mn⁴⁺ Doped K₂SiF₆—0.75% Mn—by Semi-ContinuousFlow Process Procedure

The reactor is initially charged with a solution of KF or potassiumbifluoride in HF. The initial charge may also include K₂MnF₆. Thenseparate feed solutions of K₂SiF₆ and K₂MnF₆, each in HF are started. AKF or potassium bifluoride solution in HF may be fed separately,although the KF may be included with the other solutions or in theinitial charge. After a period of about ten minutes, the feeds arestopped, and part of the mixture is removed from the reactor. Thisprocedure may be repeated multiple times.

Detailed Procedure

-   -   1. Use a 1.0 L PTFE reactor and U-shaped impeller.    -   2. Reactor lid should have three holes drilled for the three        feed tubes and a slot to allow the impeller to be centered in        the reactor.    -   3. Prepare 3 clean and dry 500 mL Nalgene bottles with mark at        appropriate fill volumes. One bottle will be marked at the sum        of the feeds for the first reaction. The other two will be the        sum of the feeds for the second, third, and further reactions.        (When the reactor is drained after each batch 120 mL of solution        will remain in reactor)    -   4. Prepare feeds according to table below.

Feed Conc/Desc. Volume Required K₂MnF₆ 1.96 g/40 mL HF  410 mL H₂SiF₆ 1mL/2 mL HF   945 mL KF 100 g/150 mL HF 342.5 mLPrime all pumps and insert tubing into reactor lid.

Pump Speeds Run KF H₂SiF₆ K₂MnF₆ Drain Amount 1 5 24.7(40 s)/12.7 4.7218 mL 2 13.5 5.7 290 mL 3 293 mL 4 5.9 5 6 6.1 295 mL

-   -   5. For first run, charge reactor with KHF₂ (120 mL) and 0.84 g        Mn. With stirrer on at 250 RPM, start pumping only Si feed at        24.7 mL/min. After 40 s, change to 12.7 mL/min. At 1 min, start        KF and Mn feeds. Run with all feeds until 9 min 30 s. Stop Mn        and KF at 9 min 30 s. At 10 min stop Si feed.    -   6. When all feeds are stopped, drain reactor in to Nalgene        bottle so that only 120 mL remains in reactor (drain 218 mL).        Cap bottle and set aside.    -   7. Change speeds on Si and Mn feeds for second reaction. Start        all feeds and run for 12 min. After ten minutes repeat draining        procedure (drain 290 mL). Set aside and repeat for batch three        and four.    -   8. While batch four is running, begin filtration by decanting        and pouring PFS into filter. Filter all three batches together.        Rinse until pH reads 5.5 and set aside to dry and sift.    -   9. Drain batch four, using one of the bottles from batch 2 or 3,        set aside and run and drain batch 5 using the other bottle.        While sixth batch is running, filter batches four and five        together. Wash and set aside.    -   10. After pumps are stopped for sixth batch, prepare funnel and        completely drain reactor. Rinse as with others.    -   11. Sift all powders through 325 mesh screen.

Examples 2-3: Preparation of Mn⁴⁺ Doped K₂SiF₆ —0.75% and 1.35% Mn—bySemi-Continuous Flow Process

The procedure of Example 1 was repeated for Examples 2 and 3. The sameamounts of raw materials were used for Example 2; for example 3, theamount of Mn was increased proportionately to achieve about 1.35% Mn inthe phosphor product. Results, including particle size distribution datafor the resulting phosphors are shown in Table 2.

TABLE 2 PFS passing 325- Total mesh Oversize yield Yield sieve PFSParticle Size Example no. Mn % (gm) (gm/min) (gm) (gram) d10 d50 d90span Comparative ~0.75% 27.6 2.76 24.2 3.4 15.6 27.3 44.7 1.07 Example 1Comparative ~1.35% 30.6 3.06 26.7 3.9 18.9 27.8 39.8 0.75 Example 2Example 1 ~0.75% 239.6 6.7 237 2.6 16.2 26.7 41.6 0.95 Example 2 ~0.75%233.5 6.5 230 3.5 15.4 26.5 43.2 1.05 Example 3 ~1.35% 221.4 6.2 219.32.1 18.1 26.9 39.1 0.78

For Comparative Examples 1 and 2, it can be seen that the amount ofmaterial having particles that were larger than the openings in the 325sieve was relatively large. In contrast, for the phosphors of Examples1-3, the amount of oversize particles was greatly reduced).

Comparative Examples 4 Through 7: Synthesis in Acidic Environments

As described above, in one or more embodiments, the first solution thatcontains aqueous HF and the source of M and the second solution thatcontains the source of Mn can be gradually added to a reactor in thepresence of the source of A and an anion selected from phosphate,sulfate, acetate, and combinations thereof, to form the product liquorcomprising the Mn⁴⁺ doped phosphor of formula I, and periodicallydischarging the product liquor from the reactor. The first solution andthe second solution can be added to the reactor in the presence of thesource of A and the anion and, optionally, a cation selected from H, Li,Na, K, Rb, Cs, or a combination thereof. The first and/or secondsolution can include the H⁺ and A⁺ cations. The anion and/or cation maybe obtained from an acid and/or an acetate, such as sulfuric acid,phosphoric acid, hydrochloric acid, nitric acid, hydrobromic acid,hydriodic acid, or perchloric acid; or from potassium sulfate, apotassium acetate, or another potassium source.

Adding the anion and/or cation described above can produce LEDs havingnarrow red phosphor with better QE before any post synthesis treatments.The presence of a relatively small amount of acid during the chemicalsynthesis can maintain the desirable acidity environment for theformation of red phosphor crystals. The acidity environment alsominimizes or reduces defects within the synthesized phosphor crystal(relative to a synthesis process that does not have such an acidicenvironment). The fewer defects can lead to greater quantumefficiencies.

Example 4: Control Sample

125 g of KHF₂ was dissolved in 230 mL of 49% HF in a first beaker. Tengrams of K₂MnF₆ was dissolved in 200 mL 49% HF in a second beaker. 81 mLof 35% H₂SiF was mixed with 174 mL of 49% HF in a third beaker. Thecontents of the first, second, and third beakers were combined in areaction vessel and stirred. The precipitate was then allowed to settle,the supernatant was decanted, and 600 mL of a saturated solution ofK₂SiF₆ in 49% HF was added to the reaction vessel and stirred for 20minutes. The stirring was stopped, the supernatant decanted, and theprecipitate was vacuum filtered and dried under vacuum. The driedprecipitate was then annealed under 20% F₂/80% N₂ at 540° C. for 8hours, and stirred in 900 mL of a saturated solution of K₂SiF₆ in 49% HFfor 30 minutes. The stirring was stopped, the supernatant was decanted,and the precipitate was vacuum filtered and dried under vacuum. Theresulting dried phosphor was sifted through 270 mesh screen and the QEwas measured.

Example 5: H₂SO₄ Addition

125 g of KHF₂ was dissolved in 230 mL of 49% HF in a fourth beaker. 10 gof K₂MnF₆ was dissolved in 200 mL of 49% HF in a fifth beaker. 81 mL of35% H₂SiF₆ was mixed with 174 mL of 49% HF and 10.2 mL of 18M H₂SO₄ in asixth beaker. The contents of the fourth, fifth, and sixth beakers werecombined in a reaction vessel and stirred. The precipitate was thenallowed to settle, the supernatant was decanted, and 600 mL of asaturated solution of K₂SiF₆ in 49% HF was added to the reaction vesseland stirred for 20 minutes. The stirring was stopped, the supernatantdecanted, and the precipitate was vacuum filtered and dried undervacuum. The dried precipitate was then annealed under 20% F₂/80% N₂ at540° C. for 8 hours, and stirred in 900 mL of a saturated solution ofK₂SiF₆ in 49% HF for 30 minutes. The stirring was stopped, thesupernatant decanted, and the precipitate was vacuum filtered and driedunder vacuum. The resulting dried phosphor was sifted through 270 meshscreen and the QE was measured.

Example 6: K₂SO₄ Addition

118 g of KHF₂ and 11.4 g K₂SO₄ was dissolved in 230 mL 49% HF in aseventh beaker. 10 g of K₂MnF₆ was dissolved in 200 mL of 49% HF in aneighth beaker. 81 mL of 35% H₂SiF₆ was mixed with 174 mL of 49% HF in aninth beaker. The contents of the seventh, eighth, and ninth beakerswere combined in a reaction vessel and stirred. The precipitate was thenallowed to settle, the supernatant was decanted, and 600 mL of asaturated solution of K₂SiF₆ in 49% HF was added to the reaction vesseland stirred for 20 minutes. The stirring was stopped, the supernatantdecanted, and the precipitate was vacuum filtered and dried undervacuum. The dried precipitate was then annealed under 20% F₂/80% N₂ at540° C. for 8 hours, and stirred in 900 mL of a saturated solution ofK₂SiF₆ in 49% HF for 30 minutes. The stirring was stopped, thesupernatant decanted, and the precipitate was vacuum filtered and driedunder vacuum. The resulting dried phosphor was sifted through 270 meshscreen and the QE was measured.

Example 7: KC₂H₃O₂ Addition

118 g of KHF₂ and 7 g of KC₂H₃O₂ was dissolved in 230 mL 49% HF in atenth beaker. 10 g of K₂MnF₆ was dissolved in 200 mL of 49% HF in aneleventh beaker. 81 mL of 35% H₂SiF₆ was mixed with 174 mL of 49% HF ina twelfth beaker. The contents of the tenth, eleventh, and twelfthbeakers were combined in a reaction vessel and stirred. The precipitatewas then allowed to settle, the supernatant was decanted, and 600 mL ofa saturated solution of K₂SiF₆ in 49% HF was added to the reactionvessel and stirred for 20 minutes. The stirring was stopped, thesupernatant decanted, and the precipitate was vacuum filtered and driedunder vacuum. The dried precipitate was then annealed under 20% F₂/80%N₂ at 540° C. for 8 hours, and stirred in 900 mL of a saturated solutionof K₂SiF₆ in 49% HF for 30 minutes. The stirring was stopped, thesupernatant decanted, and the precipitate was vacuum filtered and driedunder vacuum. The resulting dried phosphor was sifted through 270 meshscreen and the QE was measured.

Table 3 below illustrates the amounts of KHF₂, HF, MnF₆, H₂SiF₆, andadditional reactants (where applicable) used to create the driedphosphors for each of the preceding Examples 4 through 7, as well as themeasured QE of the dried phosphors. The measured QE for the sampleslisted in Table 3 are normalized to the QE of the control sample (e.g.,Example 4).

TABLE 3 g g mL KHF₂/ K₂MnF₆/ H₂SiF₆/ Additional Sample mL HF mL HF mL HFreactant QE Example 4 125/230 10/200 81/174 none 100 (control) Example 5125/230 10/200 81/174 10.2 mL H₂SO₄ 102.1 Example 6 118/230 10/20081/174 11.4 g K₂SO₄ 102.3 Example 7 118/230 10/200 81/174 7 g KC₂H₃O₂103.7

As shown in Table 3, the addition of one or more anions and/or cationsfrom an acid to the solutions used to form the phosphor during thechemical synthesis of the phosphor can increase the QE of the resultantphosphor. While some additives are shown in Table 3, the list ofadditives that may be used to increase the QE of the phosphor mayinclude acids, acetates, or other substances other than those listed inTable 3.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

What is claimed is:
 1. A process for preparing a Mn⁺⁴ doped phosphor offormula I

the process comprising gradually adding a first solution comprising asource of M and HF and a second solution comprising a source of Mn to areactor, in the presence of a source of A and an anion selected fromphosphate, sulfate, acetate, and combinations thereof, to form a productliquor comprising the Mn⁺⁴ doped phosphor; and gradually discharging theproduct liquor from the reactor while volume of the product liquor inthe reactor remains constant; wherein A is Li, Na, K, Rb, Cs, or acombination thereof; M is Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Y, La, Nb,Ta, Bi, Gd, or a combination thereof; x is the absolute value of thecharge of the [MF_(y)] ion; and y is 5, 6 or
 7. 2. The process accordingto claim 1, wherein gradually adding the first solution and the secondsolution in the presence of the source of A and the anion includesadding the first solution and the second solution in the presence of thesource of A and one or more of an acid or an acetate.
 3. The processaccording to claim 1, wherein gradually adding the first solution andthe second solution in the presence of the source of A and the anionincludes adding the first solution and the second solution in thepresence of the source of A and sulfuric acid, phosphoric acid,hydrochloric acid, nitric acid, hydrobromic acid, hydriodic acid,perchloric acid, or a combination thereof.
 4. The process according toclaim 1, wherein gradually adding the first solution and the secondsolution in the presence of the source of A and the anion includesadding the first solution and the second solution in the presence of thesource of A and potassium sulfate, potassium acetate, or a combinationthereof.
 5. The process according to claim 1, wherein gradually addingthe first solution and the second solution to the reactor in thepresence of the source of A and the anion includes continually addingthe first solution and the second solution to the reactor in thepresence of the source of A and the anion.
 6. The process according toclaim 1, wherein gradually adding the first solution and the secondsolution to the reactor in the presence of the source of A and the anionincludes semi-continually adding the first solution and the secondsolution to the reactor in the presence of the source of A and theanion.
 7. The process according to claim 1, further comprising aninitial period wherein the first and second solutions are graduallyadded to the reactor without discharging the product liquor.
 8. Theprocess according to claim 1, additionally comprising precharging thereactor with a material selected from HF, the source of A, preformedparticles of the Mn⁺⁴ doped phosphor, or a combination thereof.
 9. Theprocess according to claim 1, wherein: A is Na, K, Rb, Cs, or acombination thereof; M is Si, Ge, Ti, or a combination thereof; and Y is6.
 10. The process according to claim 1, wherein the Mn⁺⁴ doped phosphorof formula I is K₂SiF₆:Mn⁴⁺.
 11. A Mn⁺⁴ doped phosphor of formula Iprepared by a process according to claim
 1. 12. A lighting apparatuscomprising a Mn⁺⁴ doped phosphor according to claim
 11. 13. A backlightdevice comprising a Mn⁺⁴ doped phosphor according to claim
 11. 14. Aprocess for preparing a Mn⁺⁴ doped phosphor of formula I

the process comprising gradually adding a first solution comprising asource of M and HF and a second solution comprising a source of Mn to areactor, in the presence of a source of A and a source of an anionselected from phosphate, sulfate, acetate, and combinations thereof, toform a product liquor comprising the Mn⁺⁴ doped phosphor, wherein thesource of the anion is an acid, an acetate, or a combination thereof;and gradually discharging the product liquor from the reactor whilevolume of the product liquor in the reactor remains constant; wherein Ais Li, Na, K, Rb, Cs, or a combination thereof; M is Si, Ge, Sn, Ti, Zr,Al, Ga, In, Sc, Y, La, Nb, Ta, Bi, Gd, or a combination thereof; x isthe absolute value of the charge of the [MF_(y)] ion; and y is 5, 6 or7.
 15. The process according to claim 14, wherein the source of theanion is sulfuric acid, phosphoric acid, hydrochloric acid, nitric acid,hydrobromic acid, hydriodic acid, perchloric acid, or a combinationthereof.
 16. The process according to claim 14, wherein the source ofthe anion is potassium sulfate, potassium acetate, or a combinationthereof.
 17. The process according to claim 14, wherein gradually addingthe first solution and the second solution to the reactor in thepresence of the source of A and the anion includes continually addingthe first solution and the second solution to the reactor in thepresence of the source of A and the source of the anion.
 18. The processaccording to claim 14, wherein gradually adding the first solution andthe second solution to the reactor in the presence of the source of Aand the anion includes semi-continually adding the first solution andthe second solution to the reactor in the presence of the source of Aand the source of the anion.
 19. The process according to claim 14,wherein: A is Na, K, Rb, Cs, or a combination thereof; M is Si, Ge, Ti,or a combination thereof; and Y is
 6. 20. The process according to claim14, wherein the Mn⁺⁴ doped phosphor of formula I is K₂SiF₆:Mn⁴⁺.
 21. AMn⁺⁴ doped phosphor of formula I prepared by a process according toclaim
 14. 22. A lighting apparatus comprising a Mn⁺⁴ doped phosphoraccording to claim
 21. 23. A backlight device comprising a Mn⁺⁴ dopedphosphor according to claim 21.